Gas nozzle for bag house cleaning systems

ABSTRACT

A reverse pulse cleaning system for use in a bag house filter including a blow tube (2) having outlet holes (3) to direct high velocity air pulses into filter bags to be cleaned. The systems includes a nozzle (1) having a control formation between the inlet and outlet ends of the nozzle. The control formation determines air flow characteristics such as velocity and direction of flow emerging from the outlet holes (3) and can improve uniformity and effectiveness of filter bag cleaning. A clampable and releasable fixing of the nozzle (1) to the blow tube allows replacement of the control formation with one of different characteristics during manufacturing or insitu fine tuning. The fixing allows the precise alignment of nozzles (1) on assembly which reduces the need for costly precision in forming the blow tube outlet holes (3). The system may include a tube (9) forming part of the nozzle with adjustable radial holes (13) to induce secondary air into the cleaning flow and may include a venturi (10) to induce tertiary air.

FIELD OF THE INVENTION

The present invention relates to cleaning arrangements for bag housefiltering systems.

BACKGROUND ART

Bag House filtering systems commonly comprise a particle collectionchamber into which air containing particles is directed in order toremove the particles therefrom. Normally provided are a plurality offilter bags extending into the particle collection chamber, eachsurrounding a clean air outlet, and are supported therein by suitablesupport cages. Air passes through the filter bags to the clean airoutlets which make connection with a clean air discharge chamber. Thefilter bags may be arranged in any desired array but are normallylocated in straight line distributions within the particle collectionchamber.

For filtering systems to work efficiently, it is necessary to repeatedlyremove particle build up on the outside of filter bags, with theparticles thus removed being collected and removed from a base zone ofthe particle collection chamber. One known arrangement for removing theaforesaid particle build up is to direct a reverse pulse of pressurisedair which passes from discharge holes in a blow tube located within theclean air discharge chamber into the mouth of each filter bag. Thereverse air pulse rapidly expands the bag to dislodge the particle buildup. To increase the air flow in the reverse pulse it has also beenproposed to use various forms of venturi arrangements on or adjacent tothe mouth of the filter bag. In one known arrangement of this kind, theventuri provided extends into the top section of the filter bag.

Known cleaning arrangements of the aforementioned kind are believed tohave a number of inefficiencies caused by differing factors. One suchfactor is apparently minor irregularities in the form of the dischargeholes in the blow tube or tubes. Further, since a free air stream tendsto expand conically, the reverse air pulse should be as accurately aspossibly positioned coaxial with, and aligned with, the central axis ofthe filter bag. Misalignment can cause a greater effect on one side ofthe filter bag than the other with the ultimate effect being that oneside of the filter bag may be over cleaned whilst the other may notreceive any cleaning effect at all.

A still further inefficiency arises from the structure of bag housefilter systems where a plurality of bag filters are supplied withcleaning air released into one end of a usual type of blow tube open atone end and closed at the other with discharge holes being located atspaced locations in line along the tube. Typically air flow volume anddirection through the first discharge hole may be vastly different toair flow volume and direction through the last discharge hole from theair supply and of the blow tube. This causes significant differences incleaning between the various bag filters supplied with reverse pulsecleaning air along the length of one blow tube.

Finally it has been recognised that in those arrangements where aventuri extends into a filter bag, zones of the filter bag adjacent tothe venturi outlet will not have full cleaning effect from a reversepulse air flow.

Variations in the uniformity of cleaning arrangements of theaforementioned kind have the effect of requiring increased filter bagfiltering surface areas and/or increased levels of consumption ofreverse pulse air flow. This has the effect of increasing the size andcapital costs of any bag house filter installation as well as increasingoperating costs (due in part to decreased bag life) because of theincreased reverse pulse air flows.

OBJECT OF THE INVENTION

The present invention has for its objective, the provision of a cleaningsystem, or of parts of a cleaning system, for a bag house filter whichwill minimise variations in cleaning or increased costs caused by one ormore of the aforementioned factors.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides a nozzle fora bag house cleaning system, said nozzle being of the type to direct airexiting from a blow-tube, said nozzle having an inlet port at one end,and an outlet port at another end and a passage there between,characterised in that said inlet port is of cross sectional area greaterthan the cross sectional area of the smaller of the outlet port or saidpassage, the smaller cross sectional area being defined as a controlformation for the nozzle which defines a flow characteristic of thenozzle.

A flow characteristic can include, but is not limited to any one of or acombination of the following: the direction of the flow; the volumetricflow rate; velocity or speed of the flow; the velocity profile of theflow; the shape of the air stream exiting the nozzle; the capacity orcapability of the flow.

The nozzle can be a single piece nozzle or it can also be, for example,a nozzle assembly which includes a nozzle insert which includes theinlet, outlet and the control formation. Throughout the specificationand claims, the words "nozzle" and "nozzle assembly" can beinterchanged.

According to another aspect, the present invention provides a nozzle fora bag house cleaning system, the nozzle of the type to direct airexiting from a blow tube, the nozzle having an inlet port at one end,and an outlet port at the other end and a flow control formation locatedat either end or therebetween to cause air flowing therethrough toassume a predetermined flow characteristic.

This nozzle can be further characterised in that said inlet port has across sectional area which is different to that of the cross sectionalarea of the outlet port or said control formation.

According to a further aspect, the present invention provides a nozzlefor directing a pulse of air into a filter bag in a bag house filteringsystem, the nozzle having a passage connecting an inlet end to an outletend, the inlet end being adapted to be connected to an outlet hole of ablow tube and having an effective cross sectional area larger than thecross sectional area of the outlet hole. Conveniently a seal meansprovides a sealing effect at an outer surface of the blow tubesurrounding the outlet hole. Such an arrangement permits the outletholes in a blow tube to be relatively large and conventionally drilledwithout any need to precisely locate and finish the holes. Because ofthe relatively large size of the holes they will not have an adverseeffect on discharge coefficients and flow efficiencies from the nozzles.The tolerances on positioning and alignment of the discharge holes canbe increased. Preferably the blow tube outlet hole has a cross sectionalarea which is at least 15% greater than the cross sectional area of theinlet end of said nozzle.

According to a further aspect of the present invention, there isprovided a mounting system for securing a nozzle to a blow tube in a baghouse cleaning system, the nozzle adapted to direct air into a mouthzone of a filter bag, the mounting system including releasable securingmeans which, when released, allows the nozzle to be aligned relative tothe mouth zone of the filter bag or allows removal of the nozzle fromthe blow tube, or allows an internal component of the nozzle to bereplaced.

When the nozzle is released an internal component such as a nozzleinsert can be replaced or the whole nozzle removed and replaced withanother. Such arrangement allows the nozzle, or any individual nozzle inan array of such nozzles secured to a blow tube, to be correctly aligned(circumferentially with respect to the blow tube). Preferably thereleasable securing means further permits axial adjustment relative tothe blow tube to allow for correct positioning relative to the filterbag mouth zone. Conveniently a venturi might be provided aligned withand located outwardly of the filter bag mouth zone and in which case,the axis of the nozzle would optionally be aligned with the axis of theventuri. By adjusting the nozzle into the best possible alignment,optimum cleaning from that alignment will result.

According to a still further aspect, the present invention provides areverse pulse cleaning system comprising a nozzle or a nozzle assemblyfor connection to a supply of compressed primary air, said nozzleassembly including passage means for a flow of secondary air to entersaid nozzle assembly and augment with said primary air. It is preferablethat the passage means comprises a port or ports which can haveassociated therewith a control or restriction means to vary the size ofthe ports, to enable controlling the amount of secondary air enteringsaid passage means. The passage means may allow entry of secondary airbefore or after the primary air exits a nozzle outlet which isassociated with a control formation.

A passage means can also be provided to enable a flow of tertiary air toenter the stream passing from or through said nozzle assembly.

Preferably said tertiary air and the combined said primary and secondaryair stream combine in a venturi.

According to yet another aspect of the present invention, there isprovided a reverse pulse cleaning system comprising at least one blowtube adapted for connection to a supply of compressed air and having aplurality of outlet holes therein, which in use direct air towardsfilter bags, and at least two nozzles associated with the outlet holes,wherein one of the nozzles includes a control formation which isdifferent to that of the other nozzle or nozzles.

Preferably, the nozzles are releasably secured to the or each blow tube.By this arrangement it is possible to provide nozzles having selectedcontrol formations permitting substantially equal flow into each bagregardless of its position along the blow tube or in the system.Releasability of the nozzles allow the nozzles of the system to beadjusted if necessary to optimise air flows. These adjustments can bemade at the time of installation or after the bag house has beencommissioned, at which time further fine tuning adjustments may beaccomplished.

Preferably said system also utilises secondary air added to an airstreampassing through said nozzle, before said airstream passes out of saidnozzle.

Preferably said system includes at least one venturi located outside ofthe filter bag through which said airstream passes before entering afilter bag to clean same.

Preferably the last such venturi through which air passes beforeentering the mouth of a filter bag has a maximum cone angle of 20°.

Preferably said system utilises a nozzle having a minimum crosssectional area which is used to modify the flow characteristics of thesystem at respective outlet holes of said blow tube.

Preferably each one of said outlet holes of said blow tube is of a sizewhich has no effect on a discharge coefficient of the respective nozzleassociated with each hole.

Preferably the CSA (cross sectional area) of the outlet hole of the blowtube is less than the effective CSA of the inlet to the nozzle.

Preferably the CSA (cross sectional area) of the inlet of the nozzleinsert is less than the CSA of the blow tube outlet hole and theeffective inlet to the nozzle.

Preferably the CSA (cross sectional area) of a control formation of thenozzle insert or nozzle is less than the CSA of the inlet of the nozzleinsert or nozzle. The control formation can be the outlet, the inlet orlocated adjacent or next adjacent thereto.

According to a further aspect of the present invention, there isdisclosed a nozzle assembly for a bag house cleaning system, the nozzleassembly being adapted to be attached to a blow tube and includes anexchangable flow control means to permit substitution by another flowcontrol means having a different control formation to control airpassing through the nozzle assembly.

According to a further aspect of the present invention, there isdisclosed a nozzle assembly for a bag house cleaning system, the nozzleassembly being adapted to be attached to a blow tube and including avariable air flow control means, the variable air flow control meansbeing at least one adjustable secondary air inlet port which controlsinduction of secondary air into the nozzle assembly.

According to a further aspect of the present invention, there isdisclosed a nozzle assembly for a bag house cleaning system, the nozzleassembly being adapted to be attached to a blow tube and including atleast one secondary air inlet port which allows induction of secondaryair into the nozzle assembly upstream of an outlet associated with acontrol formation in the nozzle assembly.

According to a further aspect of the present invention, there isdisclosed a nozzle assembly for a bag house cleaning system, the nozzleassembly being adapted to be attached to a blow tube and having an airflow control means, being at least one secondary air inlet port whichallows induction of secondary air into the nozzle assembly after airflow exits an outlet associated with a control formation.

By providing the nozzle assembly with replaceable nozzle inserts, orvariable secondary air inlet ports, a number of standard nozzle insertholders can be provided and inserts selected at the point ofinstallation. Otherwise, the size of the secondary air inlet ports canbe adjusted on site, after assembly. This makes the manufacture anddesign of whole bag house cleaning systems a process which can beperformed at a location which is not the site of the bag house, andfinal "tuning" of the system can be made a relatively easy task.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 illustrates a bag house cleaning apparatus according to a firstembodiment of invention in sectional view;

FIG. 2 illustrates a detailed sectional view of part of the apparatus ofFIG. 1;

FIGS. 3A and 3B illustrate, respectively, elevational and sectionalviews of a seal for use with the apparatus of FIG. 1;

FIG. 4 illustrates a strap for use with the apparatus of FIG. 1;

FIG. 5 illustrates a detailed sectional view of a second embodiment ofthe present invention;

FIG. 6 illustrates a detailed sectional view of a third embodiment ofthe present invention;

FIG. 7 illustrates a detailed sectional view of a fourth embodiment ofthe present invention;

FIG. 8 illustrates a detailed sectional view of a fifth embodiment ofthe present invention;

FIG. 9 illustrates a detailed sectional view of a sixth embodiment ofthe present invention;

FIG. 10 illustrates a detailed sectional view of a seventh embodiment ofthe present invention;

FIG. 11 illustrates a sectional view of an alternative nozzle adaptor;

FIG. 12 illustrates an alternative attachment means to the apparatus ofFIG. 2;

FIG. 13 illustrates a further alternative attachment means to theapparatus of FIGS. 2 and 12;

FIG. 14 illustrates in schematic view, a blow tube incorporating anembodiment of the present invention;

FIG. 15 illustrates a sectional view of an alternative seal means to theseal of FIG. 3;

FIG. 16 illustrates a plan view of the seal of FIG. 15;

FIG. 17 illustrates in sectional view an alternative seal means to theseals of FIGS. 3 or 15.

FIG. 18 illustrates an plan view of the seal of FIG. 17.

DETAILED DESCRIPTION OF THE DRAWINGS

Illustrated in FIG. 1 is a bag house filter cleaning apparatus whichincludes a nozzle assembly 1 attached to a blow tube 2, which has a blowtube outlet hole 3, which is in fluid flow communication with a nozzleinsert 4.

The nozzle insert 4 can be removably located in a nozzle adaptor 5 whichis adjustably positioned and retained against the blow tube 2, by meansof a strap 6, a locking cap screw 7 and a strap connector 8.

The nozzle adaptor 5 has connected to it a nozzle tube 9. Nozzle tube 9passes into a venturi 10, the exit end 11 of which engages the mouth ofa filter bag (not illustrated). The filter bag is attached to exit end11 by any conventional manner so that the air stream coming out ofventuri 10 will act upon the whole of the filter bag. The cone angle ofthe venturi 10 is 20°, but angles in the range of 5° to 25° can be used.

Between blow tube 2 and nozzle adaptor 5 is a specially formed seal 12,which seals the blow tube outlet hole 3 to the inlet 15A of the nozzleassembly 1. The seal 12 is of a simple construction, yet its flexibilityallows it to be adapted to a variety of blow tube sizes and a variety ofoutlet hole sizes 3 in the blow tube 2. The seal 12 can be formed fromany appropriate material having sufficient flexibility, such as rubber,neoprene and the like. The periphery of blow tube outlet hole 3 iseffectively sealed by the seal 12 which is more clearly illustrated inFIG. 3. The seal 12 as illustrated in FIG. 3, has an angled cut awayportion 23 which allows the seal 12 to effectively operate inconjunction with different size blow tubes 2 and nozzle arrangements.

The nozzle tube 9 has provision, by means of circumferentiallypositioned secondary air inlet ports 13, to allow induction of secondaryair into the nozzle assembly 1. The secondary air inlet ports 13 can beadjustably occluded by a variable throttling means (described later inrespect to FIG. 9). As primary plus secondary air exits the nozzle tube9, further air, termed "tertiary" air may be induced into the air flowthrough a gap located around nozzle tube 9 and between the entrance toventuri 10. This gap is indicated by the presence of arrows 14 showingthe direction of tertiary air entry.

More clearly illustrated in FIG. 2 is the relationship between the blowtube outlet hole 3 and the nozzle insert 4. The blow tube outlet hole 3,is clearly illustrated larger in size than the nozzle insert inlet port15 of the nozzle insert 4. The "effective" cross sectional area of theinlet 15A to the nozzle assembly 1 is defined by the inside diameter ofthe seal 12, which is larger than the blow tube outlet hole 3.

The provision of a blow tube outlet hole 3 being larger than the nozzleinsert inlet port 15, will, during a bag cleaning phase, result inextremely high velocity air coming out of the blow tube hole 3 havingits direction and flow rate characteristics properly controlled by thenozzle insert 4. Some of the other characteristics that can becontrolled include the volumetric flow rate, the velocity or speed ofthe flow, the pressures, the velocity profile, the share of the airstream exiting the nozzle and the flow capacity and capability. This isin contrast to prior art systems, in which air exited the holes in ablow tube with unequal and inconsistent velocity, the absence of precisecontrol of the flow rate and direction leading to unequal andinconsistent cleaning of the filter bags.

As air passes in use through the nozzle insert 4, and exits same throughoutlet port 16, secondary air is drawn in through secondary air inletports 13 around the circumference of the nozzle tube 9. This air streamcan be further increased by induced tertiary air which enters the systemin the direction of arrows 14 (see FIG. 1) as the air exits the nozzletube 9 and enters the venturi 10. By the addition of secondary andtertiary air an increase in the volume of air of a factor of up to 2 to1 to 3 to 1, can be added to the airstream entering the venturi 10 whencompared with air exiting the blow tube 2.

In prior air systems discrepancies in the flow characteristics exist inthe air flow exiting at different positions along a single blow tube.With the present invention, different nozzle inserts 4 can be selectedfor these different positions having different control formations 18.The control formations 18 will be selected according to the effect thatis desired. In the illustrated embodiments the control formations 18 aremade up of appropriately sized control diameters 18 to enable evencleaning of the filter bags along any one row fed by a single blow tube.By controlling the variation between nozzles, effective cleaning willresult, and effective use of energy consumed will also result.

The nozzle assembly 1 can be clamped to the blow tube 2 by means of aretaining clip or strap 6, which is more clearly illustrated in FIG. 4.The strap 6, is made up of a flexible ribbon or strip of metal havingtwo holes 19 which engage projections 20 on nozzle adaptor 5. In thecentre of the strap 6, is a hole through which a locking cap screw 7passes. The strap connector 8 has a threaded bore 21, which engages thethread on locking cap screw 7 and allows the locking cap screw 7 to bearagainst the circumference of the blow tube 2. As locking cap screw 7 istightened, the strap connector 8 is forced in the direction of arrow 22,thereby tensioning the strap 6, and forcing the nozzle adaptor 5 towardsthe blow tube 2, thereby compressing the seal 12.

The cap screw 7 and strap connector 8 provides an arrangement to replaceor release and align the nozzle assembly 1 or to experiment withdifferent size control diameters for nozzle inserts 4.

Illustrated in FIG. 5 is a second embodiment, which is similar to thatof FIG. 1. Parts which are common with FIG. 1 have been like numbered.The nozzle insert 50 is of a different construction to the embodiment ofFIG. 1. It consists of a venturi having a control formation 51 which islocated between the inlet end 52 and outlet end 53. The inlet end 52 hasa tapered/conical passage 54 which reduces down to the control formation51. Likewise, a tapered/conical exit passage 55 connects controlformation 51 and outlet end 53.

Illustrated in FIG. 6 is a third embodiment, which is similar to that ofFIG. 1. Parts which are common with FIG. 1 have been like numbered. Thenozzle insert 60 has a control formation 61 which is located at theoutlet end 62 of the nozzle insert 60. The inlet end 64 and passage 63which connects the inlet end 64; to the control formation 61 is of aconstant size.

Illustrated in FIG. 7 is a fourth embodiment, which is similar to thatof FIG. 1. Parts which are common with FIG. 1 have been like numbered.The nozzle insert 70 of this embodiment has a control formation 71 whichis located in close proximity to the inlet end 72. The inlet end 72 isconnected by a tapered/conical passage 73 to the control formation 71.On the outlet side of the nozzle insert 70 is the outlet end 74 which isconnected by means of a passage 75 having a constant cross sectionalarea, which is a counter bore with respect to the control formation 71.

FIG. 8 represents a fifth embodiment which is constructed in a similarmanner as the previous embodiments. The nozzle assembly 80 utilises somecomponents and features which are similar to those of previousembodiments and have been like numbered accordingly. The nozzle assembly80 differs from previous embodiments in that secondary air inlet ports81 allow induction of secondary air into the air stream which will exitthe nozzle assembly 80. In this embodiment, the secondary air enters thenozzle assembly 80 via the nozzle insert 82. The nozzle insert 82 is aventuri which will draw secondary air into the air stream passingthrough the venturi. It will be noticed that the nozzle tube 9 does notinclude ports as in the other embodiments.

FIG. 9 illustrates a sixth embodiment which is similar to that of FIG.6. Similar parts have been like numbered. This embodiment includes onthe nozzle tube 9 an axially adjustable sleeve 91 which is capable ofclosing or partially closing the secondary air inlet ports 13. Thisembodiment will control the volume of the air flow exiting the nozzleassembly by controlling the amount of secondary air which will enter theair stream. This embodiment may be utilised with a single size of nozzleinsert 60, which need not vary in the bag house. As the flowcharacteristics can be controlled at individual nozzles, each nozzle canbe fine tuned to adjust for its position along the blow tube.Alternatively instead of using an adjustable sleeve 91 some of thesecondary air inlet ports 13 may be fully or partially closed off bymeans of any suitable plug or cover such as a sleeve with like secondaryair inlet ports 13 which is rotated on nozzle tube 9 rather than axiallymoved. The nozzle tube 9 can also be provided, at the point ofmanufacture or another location, with a predetermined number of holes ofselected sizes according to the range of flow characteristics which areto be achieved.

FIG. 10 illustrate a seventh embodiment which is similar to that of FIG.6. Similar parts have been numbered with like numerals. This nozzleassembly 100 is constructed from three components. A nozzle tube 9 isswaged at 105 (or other cold forming process) onto a groove 106 on thenozzle adaptor 101. The nozzle adaptor 101 also incorporates the nozzlecomponents of the inlet passage 102, outlet passage 103 and the controlformation 104, which are all integrally moulded. FIG. 10 alsoillustrates a seal 12 which is the third component. As a furtherpossibility (not illustrated),by integrally moulding the nozzle adaptor101 with the nozzle tube 9 and including the nozzle air passages andcontrol features, only a seal 12 will need to be added, in order toproduce a functional two piece nozzle assembly (excluding mountingmeans).

If a one piece construction is required (that is to remove the need fora separate seal 12), a nozzle adaptor 110 as illustrated in FIG. 11 canbe utilised. The a nozzle adaptor 110 has a curved inlet end 111 whichcan be attached directly to a blow tube with out the need for a seal.Whilst some leakage may occur, it will not be significant enough toaffect the performance and operation of the bag house system. Thepreferred materials for the construction of the nozzle components isaluminium or an alloy thereof, however any suitable material can beutilised. For example, if a single piece nozzle assembly is moulded outof plastics material, and the curved inlet end 111 is also incorporated,then, if a material having some flexibility is selected, the curvedinlet end 111 will make satisfactory seal with the blow tube to which itis connected.

As a further possibility (not illustrated) the nozzle tube and nozzleadaptor may be moulded as one piece into which a nozzle insert therequired control formation can be inserted, as can a seal if required.

Illustrated in FIG. 12 is an alternative attachment mechanism toreleasably secure the nozzle assembly 1 to the blow tube 2. Thismechanism comprises a yoke member 120 having straps 121 and 122 toconnect the yoke member 120 to the nozzle adaptor 5. Once the straps 121and 122 have been loosely assembled, the lockable bolt or locking capscrew 7 is turned to effectively secure the nozzle assembly to the blowtube 2.

Another attachment mechanism is illustrated in FIG. 13. A nozzle adaptor130 having at one side a pinned arm 131 and on the diametricallyopposite side a pinned bolt 132. Both pinned connections allow rotationof the respective components. The pinned arm 131 terminates in a sectionhaving a bore to receive the pinned bolt 132. The nozzle is secured tothe blow tube 2 by the tightening of the nut 133 on pinned bolt 132.Allowance may need to be made, to take into account any rotation whichmay result, as the nut 133 is being tightened.

Illustrated in FIG. 14 is a side view of a blow tube 2 which has mountedthereon at least two nozzle assemblies 141 and 142. These nozzleassemblies are secured to the blow tube by any of the means previouslydescribed, however those means are not illustrated here for the sake ofconvenience. The control diameter or area of nozzle assembly 141 isgreater than that of nozzle assembly 142 as nozzle assembly 142 iscloser to the blanked off end 143 of the blow tube 2. The control areaof the nozzle assembly 142 is selected to modify the characteristics ofthe air flow exiting the nozzle assembly 142 so that it is substantiallythe same as the flow exiting the nozzle assembly 141. In some situationsthis may be reversed, that is, the larger control area of the nozzleassembly will be located furthest away from the supply or source ofcompressed air.

Illustrated in FIGS. 15,16 and 17,18 are seals 150 and 160,respectively, which are alternatives to the seal 12. The seals 150 and160 have curved sealing surfaces 152 and 161 on their periphery, so thata more precise seal can be effected to the circumference of the blowtube 2. Locating projections 153 and 163 are also provided on the seals150 and 160, to prevent rotation of the seal as the nozzle assembly isbeing mounted to the blow tube. Seal 150 can be used for smallerdiameter blow tubes, whilst the seal 160 is better adapted for use withlarger diameter blow tubes. The seals 150 and 160 have the same outsidediameter, as the nozzle assemblies are preferably of only one or twosizes, with each size accepting the same outside diameter seal, with theinside diameter of the seal being selected according to the size of theinlet end of the nozzle insert or the nozzle assembly 1. In the case ofseal 150 in FIGS. 15 and 16, as the outside diameter of the pipe is lessthan the outside diameter of the seal the angular surfaces 151 areprovided to terminate or trim the curved sealing surface 152. If suchseals 150 and 160 are utilised (that is having a curved sealingsurface), a different seal will be needed to match pipes of differentdiameters (unlike the seal 12 which can be utilised with pipes ofdiffering diameters), as the curved surface will be designed to suitonly one diameter pipe.

A bag house cleaning system which ineffectively cleans means that thetotal surface areas of the bags utilised in the bag house are not alwaysbeing cleaned and this forces the air to be pumped through at a higherrate in order to maintain the same output of air for which the systemwas designed.

The ability to easily change a nozzle, nozzle assembly or nozzle insertsstems from the novel manner in which the nozzle assemblies are"strapped" to the blow tube. Further advantages stem from the use of astrapping system in that the alignment of the exit of the nozzleassembly into the venturi can be adjusted. This alignment is a factor inthe effective operation of reverse pulse cleaning systems. The use of anoversize outlet hole in the blow tube together with the strappingsystems allows the adjustment of the direction of the discharge from thenozzle assembly.

As has been mentioned previously, the use of different size nozzles ornozzle inserts allows the bag house cleaning system to produce asubstantially uniform cleaning effectiveness, regardless of thepositioning of the filter bag, by providing air flow with appropriatecharacteristics (quantity, velocity and direction) into the filter bags.The invention well demonstrates that the effectiveness of a bag housecleaning system resides in large measure in the provision of appropriateand accurately directed and shaped air flow into the filter bags,providing a minimum amount of variation between respective bags and fromend to end of any one bag. This uniformity can in fact be achieved byvarying the amount of air which enters the air stream as secondary air.The variation can be achieved by the provision of nozzles havingdifferent sizes of secondary air ports, or in the alternative, secondaryair inlet ports whose size of openings are adjustable or controllable.

Modifications by those skilled in the art can be made to the inventionwithout departing from the scope thereof. For example any of thefeatures described above can be combined with each other.

I claim:
 1. A filter cleaning system including: a blow tube throughwhich cleaning air flows, said blow tube having an outlet hole throughwhich said cleaning air may exit said blow tube; a gas nozzle includinga body having opposite ends and an air passage therethrough, said airpassage having an inlet end and an outlet end, means for coupling saidbody on said blow tube with said inlet end of said air passage incommunication with said outlet hole, said inlet end of said air passagehaving a cross sectional area greater than that of said outlet hole; andsealing means engageable with one of said opposite ends of said body atthe inlet end of said air passage and with said blow tube to provide aseal between said inlet end of said air passage and said outlet hole. 2.The filter cleaning system according to claim 1 wherein said air passageis formed by an insert accommodated in said body and said deformablesealing means engaging said insert to provide a seal between said insertand said outlet hole at said one of said opposite ends.
 3. The filtercleaning system according to claim 2 wherein said insert projects beyondthe other of said opposite ends of said body.
 4. The filter cleaningsystem according to claim 1 including air flow control means within saidair passage for producing a predetermined flow characteristic of airflowing through said air passage.
 5. The filter cleaning systemaccording to claim 4 wherein said flow control means is exchangeable foranother flow control means which produces a different predetermined flowcharacteristic of air flowing through said air passage.
 6. The filtercleaning system according to claim 6 wherein said air flow control meansis adjacent one end of said air passage.
 7. The filter cleaning systemaccording to claim 1 including secondary air supply ports incommunication with said air passage between the inlet and outlet endsthereof.
 8. The filter cleaning system according to claim 7 wherein saidair passage has a venturi configuration adjacent the communication ofsaid secondary air ports with said air passage.
 9. The filter cleaningsystem according to claim 7 including means for selectively opening andoccluding said secondary air supply ports.
 10. The filter cleaningsystem according to claim 9 wherein the means for selectively openingand occluding said secondary air supply ports comprises a sleeve movablymounted on said tube.
 11. A filter cleaning system including: a blowtube through which cleaning air flows, said blow tube having an outlethole through which said cleaning air may exit said blow tube; a gasnozzle including a body having an air passage therethrough, said passagehaving an inlet end for receiving air exiting said blow tube and anoutlet end for discharging air flowing through said air passage; meansfor coupling said body to said blow tube with said inlet end of said airpassage in communication with said outlet hole; and air flow controlmeans occupying said air passage between its ends for producing apredetermined flow characteristic in air flowing through said airpassage.
 12. The filter cleaning system according to claim 11 whereinsaid air flow control means is adjacent one end of said passage.
 13. Thefilter cleaning system according to claim 11 wherein said air passagecomprises a tubular member removably accommodated in said body.
 14. Thefilter cleaning system according to claim 13 wherein said tubular membermay be withdrawn from said body and replaced by another tubular member.15. A filter cleaning system including: a blow tube through whichcleaning air flows, said blow tube having an outlet hole through whichsaid cleaning air may exit said blow tube; a gas nozzle including a bodyhaving a bore; a tubular member removably accommodated in said bore andforming an air passage through said body, said air passage having anoutlet end and an inlet end; means for coupling said body on said blowtube with said inlet end of said air passage in communication with saidoutlet hole, said inlet end of said air passage having a cross sectionalarea greater than that of said outlet hole; sealing means engageablewith said body at the inlet end of said air passage and with said blowtube to provide a seal between said inlet end of said air passage andsaid outlet hole; and air flow control means occupying said tubularmember and through which air traversing said air passage must flow, saidair flow control means being configured to produce a predetermined flowcharacteristic of air flowing through said air passage, said tubularmember being removable from said body for replacement by another tubularmember having air flow control means operable to produce a differentpredetermined flow characteristic of air flowing through said airpassage.
 16. The filter cleaning system according to claim 15 whereinsaid air flow control means occupies said tubular member adjacent thatend thereof which is adjacent said blow tube.
 17. The filter cleaningsystem according to claim 15 wherein said air control means occupiessaid tubular member adjacent that end thereof which is remote from saidblow tube.
 18. The filter cleaning system according to claim 15 whereinsaid air control means occupies a position within said tubular membersubstantially midway between its ends.
 19. A gas nozzle solely for afilter cleaning system which includes a blow tube through which cleaningair flows, said blow tube having an outlet hole through which saidcleaning air may exit said blow tube; said gas nozzle comprising a bodyhaving opposite ends and an air passage therethrough, said air passagehaving an inlet end and an outlet end, means for clamping said body onsaid blow tube with said inlet end of said air passage in communicationwith said outlet hole, said inlet end of said air passage having a crosssectional area greater than that of said outlet hole; and sealing meansengageable with one of said opposite ends of said body at the inlet endof said air passage and with said blow tube to provide a seal betweensaid inlet end of said air passage and said outlet hole; said airpassage is formed by a tubular insert accommodated in said body and saidtubular insert projects beyond that end of said body which is remotefrom the inlet end of said air passage.
 20. A gas nozzle solely for afilter cleaning system which includes a blow tube through which cleaningair flows, said blow tube having an outlet hole through which saidcleaning air may exit said blow tube; said gas nozzle comprising a bodyhaving opposite ends and an air passage therethrough, said air passagehaving an inlet end and an outlet end, means for clamping said body onsaid blow tube with said inlet end of said air passage in communicationwith said outlet hole, said inlet end of said air passage having a crosssectional area greater than that of said outlet hole; and sealing meansengageable with one of said opposite ends of said body at the inlet endof said air passage and with said blow tube to provide a seal betweensaid inlet end of said air passage and said outlet hole; air flowcontrol means occupying said air passage for producing a predeterminedflow characteristic of air flowing through said air passage and whereinsaid air flow control means is substantially midway between the ends ofsaid passage.
 21. A gas nozzle solely for a filter cleaning system whichincludes a blow tube through which cleaning air flows, said blow tubehaving an outlet hole through which said cleaning air may exit said blowtube; said gas nozzle comprising a body having opposite ends and an airpassage therethrough, said air passage having an inlet end and an outletend, means for clamping said body on said blow tube with said inlet endof said air passage in communication with said outlet hole, said inletend of said air passage having a cross sectional area greater than thatof said outlet hole; and sealing means engageable with one of saidopposite ends of said body at the inlet end of said air passage and withsaid blow tube to provide a seal between said inlet end of said airpassage and said outlet hole; a tube connected to said body inprolongation of said air passage and in communication with said outletend of said passage, said tube having secondary air supply portstherein.
 22. A gas nozzle solely for a filter cleaning system whichincludes a blow tube through which cleaning air flows, said blow tubehaving an outlet hole through which said cleaning air may exit said blowtube; said nozzle including a body having an air passage therethrough,said air passage having an inlet end for receiving air exiting said blowtube and an outlet end for discharging air flowing through said airpassage; means for coupling said body to said blow tube with said inletend of said air passage in communication with said outlet hole; and airflow control means occupying said air passage between its ends forproducing a predetermined flow characteristic in air flowing throughsaid air passage, said air flow control means being locatedsubstantially midway between the ends of said air passage.